The metallic elements used for making aircraft, notably the front structures such as the leading edges of the flying surfaces, the flaps, the frameworks of radomes or canopies, are usually protected by a finishing coating exhibiting the physical properties required for resisting heat, to corrosion and erosion due to the impact of particles at a high speed, such as atmospheric dust particles, ice or snow crystals. Moreover, such a finishing coating meets aesthetics or camouflage requirements according to whether it is applied to commercial aircraft or to military aircraft.
These various requirements lead to the use of paints which form, on the exterior metallic structure of the aircraft, once dry, a film formed of a dielectric material exhibiting the disadvantage of the building-up of electrostatic charges during flight.
The building-up of electrostatic charges on the structure of an aircraft leads to the appearance of electric dicharges which generate, on the one hand, radioelectric interferences detrimental to the good operation of the radio-navigation and radio-communication units on board the aircraft and, on the other hand, disturbances of the electrical circuits of the on-board equipment.
In the present state of the art, the antistatic protection of aircraft consists only in rendering, to some extent, equipotential their external structure by providing, under the layer of finishing paint, the electric continuity of the metallic structures, by treating in a specific manner local dielectric surfaces such as the windshield, the radomes, and the aerial stream-lined shields, and/or by installing high performance static discharges, such as those described in U.S. patent application Ser. No. 986,587 filed Apr. 14, 1978 in the names of Jean-Louis BOULAY and Roland HOARAU, assigned to ONERA.
Such measures, which bring about a great improvement in the operational conditions of the radio equipment on board aircraft, are, however, insufficient for completely suppressing the radioelectric disturbances. Thus, researcher has been carried out, without total success, for solving this problem with new means adapted for being used alone or in combination with known means.
The research carried out by the applicants for overcoming the radioelectric interferences or noise of electrostatic origin have led them to create and develop simulation experiments on the ground of the electrization phenomena appearing in flight of the aircraft. These experiments consist in using an electrostatic charges generator, such as the one described in U.S. Pat. No. 4,228,479 dated Oct. 14, 1980 in the names of Serge LARIGALDIE and Jean CARIOU, assigned to ONERA and by which it is possible to project on the structures to be studied unipolarcharges carried by ice micro-particles. These experiments have demonstrated the existence of surface electric discharges, so-called creeping discharges, which appear locally and surprisingly on the painted metallic structures and which generate spurious electric signals. These spurious signals in the experiment, compared to the spurious or noise signals recorded in flight, confirm the existence, in flight of an aircraft, of creeping discharges.
Such simulation experiments have also demonstrated that the sparking activations, or flash-overs, appear under certain conditions between the external surface of the paint, forming a dielectric coating, and the underlying metallic structure and generate a noise of the impulsional type causing an increase of the general radioelectric noise level. Moreover, such flash-overs are prejudicial to the physical behavior of the finishing layer.